Porous polymeric materials have been produced by photo- or thermal polymerization of water-in-oil emulsions, having a relatively high ratio of water to oil phases. These emulsions, known as high internal phase emulsions (HIPEs) when the water phase is 74% or more of the total by volume, comprise a polymerizable oil continuous phase and a crosslinking agent, and a co- or discontinuous aqueous phase. To achieve the most uniform morphology, such emulsions are prepared by controlled addition of the aqueous phase to the oil phase under shear conditions in the presence of the emulsifier. See for example, U.S. Pat. Nos. 4,522,953 (Barby et al.), 6,462,100 (Thunhorst et al.), 6,353,037 (Thunhorst et al.) and WO 01/21693.
The resulting polymerized emulsions have a foam structure containing cavities or cells interconnected by pores in the cavity walls. By choosing the appropriate component and process conditions, HIPE polymers with void volumes of 74% to greater than 95% can be achieved. These materials have a high capacity for absorbing and retaining fluids. Modifications of HIPE polymers have been described: U.S. Pat. No. 4,536,521 (Haq) discloses that HIPE polymers may be sulfonated to produce materials that have a high capacity for absorption of ionic solutions.